type
   TForm1=class(TForm)
   public
     procedure FastOnBeforePrint(.......);
     procedure PrepareReportForPrint(.....);
   end;

procedure TForm1.FastOnBeforePrint(.....);
begin
   //  do some
end;

procedure TForm1.PrepareReportForPrint(.....);
var AReport:TFastReport;
begin
   AReport:=TFastReport.Create();
   AReport.LoadFromStream(.....);
   AReport.OnBeforePrint:=FastOnBeforePrint;
   //  do some
end;